iflBitArray(3) — IRIX 6.5.3f



iflBitArray(3)    Image Format Library C++ Reference Manual     iflBitArray(3)



NAME
     iflBitArray - limited subscriptable bit array class

INHERITS FROM
     none, standalone object

HEADER FILE
     #include <ifl/iflBitArray.h>

CLASS DESCRIPTION
     This class implements a very limited functionality subscriptable bit
     array that is used by the image data type converter (iflConverter).  The
     constructor requires a void* initializer, so a form such as

          int from[1024], to[1024];
          iflBitArray f = from, t = to;

     declares bit "pointers" referencing the int arrays.  The bit array can
     then be accessed with contructs of the form

          floatVal = (float)f[i];


     and deposits made with statements such as


          t[i] = floatVal;    // no cast needed



CLASS MEMBER FUNCTION SUMMARY

     Constructor


          iflBitArray(void* dp)



     Subscripted access


          iflBitArray& operator[](int idx)

          void operator=(long rhs)

          operator long()



FUNCTION DESCRIPTIONS

     iflBitArray()


          iflBitArray(void* dp)



          Constructs a bit "pointer" that accesses the bit array pointed to by

          dp.  Use the subscript operator to access elements of the array off

          this pseudo-pointer on either the left-hand or right-hand side of an

          assignment.





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iflBitArray(3)    Image Format Library C++ Reference Manual     iflBitArray(3)



     operator[]

          iflBitArray& operator[](int idx)


          The subscript operator stores the byte and bit offsets needed to
          access the element specified by idx. This function returns a self-
          reference so the real work can be done with the cast and assigment
          operators for this class.  It works with certain restrictions noted
          below.

     operator=

          void operator=(long rhs)


          The assignment operator clears or sets the bit pointed to by the
          left-hand side of the assigment.  The bit is set if rhs is nonzero,
          otherwise it is cleared.  By only allowing a long for the right-hand
          side, a bit subscript on the right is automatically extracted by
          going through the cast operator.  C++ converts other types such as
          float and short to long without complaining.

     operator long

          operator long()


          The cast operator extracts the (previously remembered) subscripted
          bit.  Again, C++ fills in all the other type conversions.

NOTES
     Due to limitations of the implementation, the same bit "pointer" must not
     occur twice in the same assignment (with different subscripts):

          t[i] = ~(long)t[j];  // bogus result (depends on order of evaluation)
          t[i] = f[j];   // ok even if 't' and 'f' point to same data array


















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